Robust digital tracking controllers for high-speed/high-accuracy positioning systems

High-speed/high-accuracy positioning is a key element in modern mechanical systems such as computer-controlled machine tools, microelectronics manufacturing equipment, mechanical manipulators, and pick-and-place devices. High-speed operations provide increased productivity and high-accuracy positioning ensures improved product quality. Robustness of positioning systems to external disturbances and parameter uncertainties provides reliability and flexibility of the system.; The objective of this dissertation is to present a design methodology for high-speed/high-accuracy position control which will yield robust performance under disturbances and parameter variations. A parameter estimation technique coupled with friction compensation is used as the first step in the design process. For robust high-speed tracking, a combination of a feedforward controller and a feedback controller is used. The feedback controller which is based on a disturbance observer compensates external disturbances, unmodeled dynamics, parameter variations, and mechanical nonlinearities. In doing so, it provides robustness and ideal feedback characteristics for feedforward controllers based on the idea of inverse systems such as the zero phase error tracking controller (ZPETC).; A major nonlinearity is due to the friction force which includes the stiction (static friction) and Coulomb friction. Through simulations and experiments, the robust tracking controller has demonstrated good tracking performance under a step disturbance and compensated well for the adverse effect due to nonlinear friction. The controller is implemented in a digital signal processing board (TMS320C30 CPU). The position-system testbed is the NSK CT-0505 X-Y table. In order to further enhance the tracking performance, a model-based feedforward friction compensator is added.; The robust controller is also implemented in the high-speed machining center (Matsuura MC510VSS). The plant includes both the velocity loop servo pack (P-control) and the feed drive system. A modified disturbance observer has been developed to accommodate the presence of an existing closed-loop servo system. By using the robust tracking controller, superior tracking performance has been achieved in tracking various trajectories which include circular, elliptical and non-circular trajectories.